OpenMRS tries to follow a common coding style in order to make our code base robust: more readable and more reliable (if the same code is created by three different developers, it should look and read very similar). Our style conventions are designed to promote consistency and good coding practices, while reducing common errors. If you feel that our coding styles could be improved (by changing, adding, or removing something), please bring your comments to the Developers Mailing List.

We use a combination of tools (checkstyle, PMD, FindBugs, ...) to write down our coding conventions in a set of rules. These rules are picked up by services (provided by our own infrastructure like SonarQube or cloud providers like codacy) so that any addition of new code (via a commit or pull request on Github) is checked for violations of these rules. Having the rules in simple config files together with the source code enable any developer to run the same checks locally.

Tools

The following tools are used to ease code review, help new developers get used to our coding style and maintain code quality.

The report will show you all the violations for each java class with their severity, the name of the rule and the location (the jxr portion in the above command enables you to navigate to the location of the violation in the java class). If you want to know more about a specific rule go to http://checkstyle.sourceforge.net/checks.html

PMD

PMD is used to check for issues like unused, unnecessary or error prone code. The PMD rules we want our code to adhere to are defined in the openmrs-core repostitory's ruleset.xml

FindBugs

Manual Run

At the moment you cannot check the code against the FindBugs rules locally using maven as with checkstyle. We are working on it

Automation

Codacy & Github Integration

We have set up integration with codacy so that our rules will be checked on every pull request. Whenever you make a pull request your code will be commented by codacy and if its clean the check will pass and if not show you what parts of your code violated which rules. You can see the current status of the openmrs-core at https://www.codacy.com/app/openmrs/openmrs-core/dashboard

SonarQube

SonarQube checks the openmrs-core code once a day. You can find the issues it found here

Limitations & Work In Progress

We aim to bring all our rules (FindBugs, ESLint) into the openmrs-core repository and to let codacy use both set of rules to check the code. Codacy is currently configured to read our checkstyle and PMD rules from the repository to check Java code that goes into it.

Other languages such as javascript, ruby, ... might be checked as well but we do not yet have formalized these rules into config files like ESLint or JSHint. If you want to do that go ahead!

FindBugs rules will not be checked by codacy since that is a feature only available to enterprise users. If you know another cloud provider that satisfies our needs and supports FindBugs please tell us!

Unit Tests

Conventions

The following conventions are applied to code in openmrs-core but we encourage module authors to adopt them as well.

File template

OpenMRS License Header. All code should start with the OpenMRS license header which can be found OpenMRS core repository.

File Length. Files should not exceed 2500 lines. If your class exceeds this length, consider refactoring your code to break it into more reasonably sized files. Overly large classes are harder to read.

One class per file. Do not put more than one class in your .java file(s).

Attribution

Attribution (either author or contributing authors) should not be placed into source code. When encountered, such attribution should be removed by (or with permission from) the original author(s). Contributions that require attribution (i.e., author(s) demanding attribution within the code contributions) will be graciously refused or removed from the repository.

(NOTE: this attribution-free coding policy took effect after version 1.1, so you may see some attribution in the existing code; we are gradually removing attribution from our code base)

Code Style

Include curly braces around if clauses, and loops even when there is a single statement inside, e.g instead of this

if(!someBooleanFlag)
...perform something with a one liner;

It should be this:

if(!someBooleanFlag){
...perform something with a one liner;
}

For classes that extend BaseOpenmrsObject, try not to override the equals() and hashcode() methods UNLESS based on some specific semantics you have to do so

Avoid unnecessary else statements, normally you should be able to configure your IDE to catch this and warn you about it, e.g instead of this

Use interfaces for return types that are collections that way the actual collection implementation used within a method can later be changed if need arises without breaking existing code.

When writing services, the @Transactional annotation should be added to the Implementing class at the class level and not the interface, then all methods that don't write to the database e.g getXXX methods should have their own Transactional annotation with the readOnly attribute set to true

Please check your IDE settings it is often the IDE which merges several imports into a wildcard import.

Naming Conventions

Package names should be lowercase without punctuation, following Java specs.

Class and interface names should be capitalized (using CamelCase), begin with a letter, and contain only letters and numbers.

Method names should follow Java specs.

Parameter names should follow Java specs.

Class and instance variables should follow Java specs. Any constants should be written in uppercase letters.

Strings

Concatenation

Use of StringBuffer in place of String Concatenation. Use the StringBuffer if you want to concatenate a number of string literals especially when this concatenation is not being done in a single line. e.g.Don't write like String s = ""; s+= "Hey!"; s+'=" "; s+="Bye!" ; Always write StringBuffer sb = new StringBuffer(); sb.append(Hey!); sb.append(" "); sb.append("Bye!"); String s = sb.toString();

Use of StringUtils

We have both the apache commons StringUtils and springframework StringUtils library. If possible, use the apache commons StringUtils method. However, if the spring StringUtils is already imported, use that one.

Do not comment out code

Do not leave commented out code in the source files. Just remove it. Others will think this has been left there for a purpose and thus will probably not dare to delete it which will leave this commented out code hanging around forever. There are some exceptions of course, such as: "When I'm pretty sure it needs re-enabled at some point, and to make sure I don't forget why that is, I leave a clear TODO comment, e.g. "TODO this needs re-enabled when TRUNK-XXXX is fixed". Most IDEs are good at parsing out all TODO statements." Rowan Seymour

Switch default case. All switch statements should have a default case if only to assert false, since future coding changes may introduce unexpected cases.

Switch fall through. All switch cases containing any code should end with a break or return statement to avoid accidentally falling through to the next case. In the rare case that you desire a fall through, the next case should be preceded with /* fall through */ to indicate your intention.

Magic Numbers. Literal numbers should only exist within constants, rather than being introduced directly in the code.

Literal Long Numbers. Always use a capital L for long numbers, since a lowercase L (l) is easily confused with a one (1).

equals() without hashCode(). Classes that override equals() should also override hashCode()'.

Nested If Statements. If statements should not be nested deeper than eight (8) levels.

Nested Try Statements. Try statements should not be nested deeper than three (3) levels.

No clone(). Classes should not override the clone() method.

(expression false). Do not test equality with true or false; rather, simplify the boolean expression by removing the comparison and, if necessary, adding a leading exclamation mark (!) if you are testing for false expressions.

if Statements. If statements should always be enclosed in braces. Always write "if (expr) {doSomething();}", never write "if (expr) doSomething();"

Loop Braces. There should be braces for the in the case of any loop even there is only one statement. Always write "while (condition) {doSomething();}", never write "while (condition) doSomething();"

Documentation

All classes and interfaces should, at a minimum, have a Javadoc comment at the class level

Public methods should have a Javadoc comment

Code that performs any non-obvious task should be documented for clarification

Specify the return value of every method. Return values that should be documented are: null values, empty collections (whether an empty sets or empty list is always returned, etc)

Test this return value assumption and annotate them with @should as described by Unit Tests

Please note that the commenting style from most textbooks is only a good practice when the comments are intended for a student learning to program. It is not intended for professional programmers. Take a look at these best practices for commenting your code.

Exception Handling

General

catch (Exception e) {}. Do not catch Exception, Throwable, or RunTimeException; rather, you should catch more specific exceptions. Catching these high level exceptions can mask errors.

throw Throwable. Do not throw Throwable, Error, or RuntimeException; rather, you should throw more specific exceptions.

Creating Custom Exceptions

Create an intuitive hierarchy of exceptions within the package they belong, only creating new Exception classes for when the need to branch on different types of exception within code/webapp are needed (add as needed instead of making extra classes "just in case" for every possible variation).

Patching Third Party Libraries

New Public Methods and Classes

All new public methods and classes should have a @since annotation for the version when they were introduced. If the class is new, then it is enough to just put it at the class level instead of each method. Something like: @since 2.0

Deprecation

We deprecate methods that are part of our external public interface, instead of changing/deleting them in order to preserve backwards compatibility

External, public methods include:

service methods

public interface methods

domain object methods

Internal methods are not considered public, and therefore do not have to go through a deprecation cycle, and can be changed/deleted outright. These include:

DAO methods

We will delete all deprecated methods when we make a new version (eg from 1.x to 2.0)

Use both the @Deprecated annotation and the @deprecated javadoc comment

The @deprecated javadoc annotation should point to the new method that is replacing the current one

The @deprecated javadoc annotation should also mention the version when the deprecation happened. e.g: @deprecated As of 2.0, replaced by {@link #getEncounters(EncounterSearchCriteria)}

Security

Avoiding XSS scripting

In JSPs, use a core.OutTag for every string type attribute (or even for every variable)